The ultimate goal of this project is to develop a safe and effective technique for long-term organ preservation. The specific aim of this study is to enhance glycolytic energy production during hypothermic heart storage. Despite more than three decades of extensive research, safe preservation times for the heart remain very short. This is the result of two major deficiencies: 1) the critical energy requirement for the heart during ischemia has been mostly ignored, and 2) little attention has been paid to the fact that there are many rate-limiting factors in glycolysis, and, therefore, the use of a single chemical may not be effective. The investigators propose a new approach for improving heart protection. Their general hypothesis is that hypothermic heart preservation times can be extended by enhancing glycolytic energy production. This goal is achieved by using a glycolytic intermediate, fructose-1,6-diphosphate (FDP), to bypass two ATP-consuming steps, by adding AMP precursors to facilitate ATP re-synthesis, and by using insulin to reduce lactate production. They have evidence that adding FDP to Euro-Collins or St. Thomas solution can substantially enhance hypothermic heart preservation in rats and rabbits, and that FDP can cross the cell membrane in a dose-dependent fashion. Although FDP has been used in tissue ischemia with impressive results, it has not been used in heart preservation, and studies on its mechanism of action are surprisingly superficial and scarce. The hypothesis will be evaluated using three different approaches: 1) in cardiomyocytes in normoxia and hypoxia at normal temperature and during hypothermia, 2) in hypothermic rabbit heart preservation, and 3) in rabbit and dog heart transplantation. Cardiomyocyte function, FDP uptake and metabolism, pyruvate dehydrogenase (PDH) activity, pyruvate and lactate production, and membrane and mitochondrial integrity will be examined in cardiomyocyte culture. Mechanical performance, tissue biochemical integrity, enzyme release, adenine nucleotide production and consumption, pyruvate and lactate production, and histological changes will be quantified in heart preservation. This project will greatly enhance our understanding of ischemia and tissue protection, and provide a mechanism that could significantly increase heart preservation times for transplantation. These glycolytic modulators might produce a synergistic effect and serve potentially as effective tissue-protective agents during ischemia, not only in heart preservation and cardioplegia, but also in other ischemic conditions, such as shock, stroke, coronary heart disease, and cardiopulmonary bypass.